PROJECT SUMMARY Osteoporosis, a disorder characterized by progressive, age-related decreases in bone mass and density, disruption of normal bone architecture, and consequent reduction in bone strength, results in increased susceptibility to fracture. In older persons, osteoporotic fracture is associated with substantial comorbidity and mortality. As the world's population ages, the attendant human suffering and economic costs of osteoporosis are predicted to increase dramatically. Research on osteoporosis in the developed, industrialized countries like the U.S., Canada, and the E.U. nations has elucidated the contributions of dietary, behavioral, and environmental factors to age-related fracture risks and has begun to unravel the genetic underpinnings as well. However, most searches for osteoporosis risk genes are less than optimally powered and osteoporosis-related research in developing countries is nascent or nonexistent. We propose to conduct the first combined whole genome linkage and association study for genes affecting variation in bone-related phenotypes in a population from a developing country: the Jirels of Eastern Nepal. With 2000 members already genotyped at over 400 marker loci, the single, unbroken, non-inbred Jirel pedigree currently is the largest and most powerful dataset available to a genome scanning study. (1) We will characterize all 2000 individuals for a broad range of bone-related traits including bone ultrasound attenuation of the calcaneous, bone mineral densities in 3 regions (proximal femur, lumbar spine, and forearm) assessed using dual-energy X-ray absorptiometry, and 12 biomarkers related to bone formation, turn-over, and metabolism. (2) We will use quantitative genetic analysis techniques to determine the amount of variation in each of the bone-related traits that is attributable to genes and assess the degree to which common genes influence pairs of bone-related phenotypes (pleiotropy). (3) We will conduct genome-wide linkage analysis to localize genes for each of the bone related phenotypes - as well as pleiotropic genes affecting multiple phenotypes - to specific chromosomal regions. (4) We will genotype 1000 of the participants for approximately 550,000 single nucleotide polymorphisms and use novel, pedigree-based genetic association methods to nominate and prioritize positional candidate genes for all QTLs. (5) Finally, using these same analytical methods and SNP marker sets, we will perform analyses to validate our findings in 1000 Euro-American participants of a separately funded study of the genetics of osteoporosis-related traits in the Fels Longitudinal study The goals of this project are the localization, identification, and characterization of QTLs influencing bone-related phenotypes, the nomination of positional candidate genes likely contributing to variation in these traits - and, by extension, osteoporosis population directed by co-investigators on this project. risk - in humans in general, as well as those with effects more specific to peoples from an understudied region of the world.